This invention relates to lamp tubes and, more particularly, to a lamp tube having a uniform lighting profile and to a treatment process for producing same.
Optical scanners generate machine-readable image data representative of a scanned object such as an image on a paper document or other media. Flatbed optical scanners are stationary devices which have a transparent platen upon which the media or object to be scanned is placed. Equipment such as flat bed scanners, film scanners, copiers and some digital cameras may use a linear cold cathode fluorescent lamp (CCFL) as the light source. The media or object is scanned by sequentially imaging narrow strips or scan line portions of the media or object by an imaging apparatus such as a charge-coupled device (CCD). The imaging apparatus produces image data which is representative of each scan line portion of the scanned media or object. A linear arrangement of light sensitive elements, such as CCD photodetectors, is used to convert light into electric charges. There are many relatively low-priced color and black and white, one-dimensional array CCD photodetectors available for image scanning systems. Electronic imaging systems may alternatively use two-dimensional arrays of light sensitive elements such as CCD arrays. However, these arrays are expensive because they have low manufacturing yields. Linear photodetectors cost much less than array detectors because they are much smaller and have higher manufacturing yields.
While linear CCFLs are bright, inexpensive, and reliable, they also have one major disadvantagexe2x80x94they have a non-uniform illumination intensity profile that requires corrective analog or digital gain to normalize. These devices suffer from low signal-to-noise ratios at the ends of the scan lines due to decreased light intensity on the object or media and through the optical system.
In accordance with an embodiment of the present invention, a method of treating a lamp tube having a first end and a second end comprising introducing a first quantity of a luminescent substance into the first end of the lamp tube and introducing a second quantity of a luminescent substance into the second end of the lamp tube is provided.
In accordance with another embodiment of the present invention, an illumination source comprising a linear tube having a first end and a second end and an inner surface having a luminescent substance distributed thereon, a longitudinal distribution of the luminescent substance having a minimum at a first point of the inner surface and a luminescent substance density greater than the minimum at each of a second and third point of the inner surface, the first point longitudinally located between the second and third points, is provided.